Bottom line, when you read Any Day with You, you feel awash in family love–whether multi-generational, extended, or found.
Adult secondary characters need to serve the story and the change and growth necessary for the main character. With teacher characters, as with other adults, you have a wide range of options–from allies to antagonists.
Kate O’Shaughnessy creates secondary character Tommy O’Brien in such a way that, even though the book is in Maybelle’s first person point of view, readers know things about Tommy that Maybelle doesn’t.